Effects of perturbing B-field orientation on magnetic priming of a Relativistic Magnetron

Experiments have been performed testing magnetic priming at the cathode of a relativistic magnetron to study the effects on high power microwave performance. Magnetic perturbations were imposed utilizing three, high-permeability nickel-iron wires embedded beneath the emission region of a 1.27 cm diameter cathode, spaced 120 degrees apart (for N/2 symmetry in an N (6) cavity magnetron). These three, high-permeability wires perturb both the axial and radial magnetic fields near the emission region of the cathode. Magnetic priming was demonstrated at UM to increase the percentage of p-mode shots by 15% over the baseline case in the relativistic magnetron. Improvements in microwave power, pulse width and start-oscillation time were also observed. Earlier experimental research by Neculaes and recent simulation work suggest that using permanent magnets with radially-directed remanence fields centered under the cathode emission region instead of high permeability wires can yield improved magnetron performance.